added primaryPage

etc/openapi.json

                             "maximum": 18446744073709551615
                         }
                     },
+                    "primaryPage": {
+                        "readOnly": true,
+                        "description": "Which page is the default page",
+                        "type": "string"
+                    },
                     "name": {
                         "readOnly": false,
                         "description": "Document name, may be empty",